Medullary sponge kidney and renal acidification defect.

Medullary sponge kidney ( MSK ) is one of the entities which comprises a subclass of renal cystic disorders. While the clinical signs, symptoms, and radiological findings have been well documented in the past, the literature concerning renal function in these patients is relatively sparse. Thus, the purpose of the present studies was to examine the renal function in 11 patients with MSK and compare them to seven healthy volunteers and ten control patients with bilateral renal stones. Patients with MSK had normal GFR, RPF, and capacity to dilute urine; however, their urine concentrating ability was diminished. Urine pH in MSK patients was higher than in control patients with NH4Cl administration, while titratable acid excretion was lower than normal. Steady-state plasma bicarbonate concentration was lower in MSK patients than in controls but arterial pH was within normal limits. These studies suggest that MSK patients have defects in urinary acidification and concentration mechanism which may, in part, be the result of functional abnormality of the terminal collecting ducts.